1. Field of the Invention
The present invention relates to motorcycles, and more specifically, to a motorcycle equipped with a spark arrester for reduced emission into the atmosphere of smut, etc. contained in the exhaust gas.
2. Description of the Related Art
As disclosed in JP-A Hei 10-266828, for example, a conventional motorcycle may have a mesh of spark arrester inside its silencer in order to reduce emission into the atmosphere of smut, etc., contained in its exhaust gas. The spark arrester is designed to be inserted around an open end of a tail pipe inside a silencer, so that the exhaust gas passes through the spark arrester and then into the tail pipe. In this process, smut, etc. in the exhaust gas are captured by the spark arrester.
According to the motorcycle disclosed in JP-A Hei 10-266828, the silencer includes an outer tube which constitutes an outer wall of the silencer. The outer tube has a circular section, and the spark arrester is also tubular, having a circular section like the outer tube.
The smut, etc. contained in the exhaust gas are gradually accumulated in the spark arrester. Therefore, in order to extend a period of good operating condition in which the exhaust gas makes smooth passing through the spark arrester, it is desirable that the spark arrester has a large surface area.
The surface area of the spark arrester may be increased by increasing the spark arrester's diameter. In this case, however, the outer tube must be increased in its diameter in order to provide a sufficient distance between the spark arrester and the outer tube inner surface. In the above-described conventional motorcycle, the silencer outer tube has a circular section, which means increasing the outer tube diameter leads to an increased width of the motorcycle.
The surface area of the spark arrester may also be increased by increasing the spark arrester's length. In this case, however, the outer tube must be increased in its length in order to avoid interference between the spark arrester and other members disposed inside the outer tube (such as partitioning walls for dividing the inside space of the outer tube into a plurality of expansion chambers, and pipes for connecting the expansion chambers). Generally in motorcycles, a large number of components are disposed within a tight space. Increasing the length of the outer tube increases the difficulty of the layout of the other components. In addition, a longer outer tube must be supported with stronger members.